Field devices are used in industries to control operation of a process such as that of an oil refinery. A field device, such as a process variable transmitter, is typically part of a process communication loop and is located in the field to measure and transmit a process variable such as pressure, flow or temperature, for example, to control room equipment. A field device such as a valve positioner can also be part of the process communication loop and controls position of a valve based upon a control signal received over the process control loop, or generated internally. Other types of controllers control electric motors or solenoids, for example. The control room equipment is also part of the process communication loop such that an operator or computer in the control room is capable of monitoring the process based upon process variables received from transmitters in the field and responsively controlling the process by sending control signals to the appropriate control devices. Portable communicators are often used to configure field devices coupled to the process communication loop. As used herein, the term “process communications loop” is intended to mean any physical connection and media (including a wireless process communication loop) that carries process signals, regardless of whether the connection forms an actual loop. Thus, a process communication loop can be a HART® or FOUNDATION™ Fieldbus segment, even though such a segment is not strictly considered a loop.
With the advent of low-power microprocessors, field devices have undergone significant changes. Currently, many field devices employ digital communication technology as well as more sophisticated control and communication techniques. However, field devices still often employ low-power electronics because in many installations they are required to run on as little as 4 mA. This design requirement prohibits the use of a number of commercially available microprocessor circuits. However, even low-power microprocessors have allowed a vast array of functions for such field devices.
There has been a dramatic increase in the availability of such microprocessor-based field devices. Such field devices are sometimes termed “smart” or “intelligent.” There has also been a dramatic increase in the availability of software applications that are used to configure, test, and diagnose these smart field devices. Connection of a general purpose computing device, such as a PC or a portable laptop computer is typically accomplished using a modem communicatively coupled between the computing device and the intelligent field devices. There is a significant array of process communication protocols such as the HART®, FOUNDATION™ Fieldbus, and Profibus protocols that support the various process control tasks. Moreover, it is common to find multiple communication protocols in use in the very same process installation.